policy briefNI B 12-01 | July 2012 | nicholasinstitute.duke.edu

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Greenhouse Gas Mitigation Opportunities for Livestock Management in the United StatesBased on a report by Shawn Archibeque, Karen Haugen-Kozyra, Kristen Johnson, Ermias Kebreab, Wendy Powers-Schilling, Lydia Olander,1 and Abigail Van de Bogert

This work synthesizes and communicates foundational informa-tion for designing greenhouse gas mitigation and reporting programs for livestock systems in the United States, in particular for reductions in enteric and manure methane emissions.

Changes in livestock management can ben-efit air and water quality and help to slow global climate change.2 Several efforts are under way to create incentives for greenhouse gas (GHG) mitigation from the agricultural sector. For example, the U.S. Department of Agriculture encourages management prac-tices that reduce GHG emissions in several of its incentive and extension programs. The state of California is launching a carbon off-sets market under which agriculture may be a significant supplier. And supply chain and certification programs for agricultural products associated with corporate sustainability initiatives are also exploring opportunities for GHG reductions from the agricultural sector.

Although livestock management is a small contributor to overall GHG emissions in the United States, it is a significant contributor to the total emissions from agriculture, making up more than half of such emissions in the United States.3 Most of livestock’s direct impact on global climate comes in the form of methane (CH4). Because meth-ane is roughly 20 times more potent than carbon dioxide (CO2), small reductions can have significant effects on overall emissions. Recent analysis suggests that reductions in methane and black carbon together can greatly reduce predicted near-term temperature increases and cli-mate change impacts, potentially keeping global temperatures below the well-known 2°C threshold in the near term.4

As shown in figure 1, livestock contributes around half of all agricul-tural emissions in the United States. Of this, enteric fermentation, which releases methane from animal digestion, is the largest contribu-tor from livestock, followed by emissions from manure and grazing

1. Olander is Director for Ecosystem Services at the Nicholas Institute for Environmental Policy Solutions, Duke University, and is the contact person for this brief: lydia.olander@duke.edu. For more information, visit http://nicholasinstitute.duke.edu/ecosystem/t-agg.2. P. Smith et al., “Agriculture,” in Climate Change 2007: Mitigation; Contribution of Working Group III to the Fourth Assessment Report of the Intergov-ernmental Panel on Climate Change, ed. B. Metz et al. (Cambridge: Cambridge University Press, 2007); B.A. McCarl and U.S. Schneider, “Greenhouse Gas Mitigation in U.S. Agriculture and Forestry,” Science 294, no. 5551 (2001): 2481–2482; D. Shindell et al., “Simultaneously Mitigating Near-Term Climate Change and Improving Human Health and Food Security,” Science 335, no. 6065 (2012): 183–189; C. Hellwinckel and J. Phillips, “Land Use Carbon Implications of a Reduction in Ethanol Production and an Increase in Well-Managed Pastures,” Carbon Management 3, no. 1 (2012): 27–38.3. U.S. Environmental Protection Agency (EPA), Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2009 (Washington, D.C.: U.S. EPA, 2011).4. Shindell et al., “Simultaneously Mitigating.”

Key Points

• Livestock contribute significantly to agricultural emissions in the U.S., primarily from associated land management, enteric fermentation (methane from the animal), and manure management.

• Beef, dairy, and swine production systems are by far the largest contributors to U.S. livestock emissions.

• Livestock populations and production have held relatively steady over the last decade, suggesting that changes to the management of existing systems may be more cost-effective than whole-scale shifts in production systems and infrastructure.

• Manure management may yield a greater GHG reduction at source, but enteric emissions reductions, taken across a large segment of the beef and dairy population, can create a larger overall impact on GHG emissions.

• For swine, manure management strategies are most promising. Reducing the amount of time that manure is stored in a pit and using anaerobic digestion are both likely ready for implementation where cost-effective.

• A number of programs are in development to reduce GHG emissions from livestock systems in the U.S.; some are developing offset protocols for projects, while others are focused on production systems and are conducting life-cycle assessments for certification or supply chain initiatives.

Enteric fermentation

28%

Manure management

14%

Rice cultivation 1%

Burning of residue 0%

Cropland soils 30%

Grassland soils 12%

Energy use 15%

Figure 1. Gross agricultural GHG emissions, 2009.Note: Land use change and liming of soils are not included. Sources: EPA, 2011 (note 3); USDA, 2011 (note 9).

Greenhouse Gas Mitigation Opportunities for Livestock Management in the United States

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lands.5 Within the United States in 2010, enteric fermenta-tion from livestock contributed 141.3 teragrams of carbon dioxide equivalent (Tg CO2e), accounting for 70% of the annual methane emissions associated with agricultural production systems; this is equivalent to 21% of all U.S. anthropogenic methane emissions.6 Methane emissions from livestock manure management in 2010 contributed 52 Tg CO2e, or 8% of the total. Emissions from livestock manure in the United States have increased by roughly 56% since 1990 (fig. 2), mainly as a result of the increas-ing use of liquid manure management systems, which have higher methane emissions than other management methods.7

Beef, dairy, and swine systems are the largest contributors to livestock-related greenhouse gas emissions in the United States (fig. 3).8 Livestock populations and production have held relatively steady over the last decade;9 thus, implement-ing changes to the management of existing systems may be more cost-effective than trying to effect whole-scale shifts in production systems and infrastructure. Opportunities to reduce methane emissions through changes in feed and manure management are significant, as is the potential for smaller reductions in other GHGs, including carbon dioxide (CO2) and nitrous oxide (N2O). Each livestock production system is different, and no single management change will work for every operation. However, resources identifying a suite of economically sustainable options and the impact of adoption will allow producers to identify those practices that can fit their system.

For beef and dairy cattle, a number of mitigation strategies can improve productivity by reducing methane emissions per unit of product. Improved diet and genetics can help these animals use feed more efficiently and reach maturity more quickly. Other strategies focus on reducing enteric emissions through feed additives such as ionophores and organic acids. Although limited in scale, improved pasture management holds promise for reducing methane emissions and is well enough understood to be implemented now. Other strategies need additional research; most are expected to have moderate to low mitigation potential.

For beef and dairy cattle, the most promising manure management strategies include aeration, compaction, composting, and the shift from liquid to solid systems. Aeration and shifting from liquid to solid systems are likely to be expensive. The mitigation potential and financial viability of these strategies require further research. The most well-studied high-potential activity is use of a digester for methane capture and flaring or combustion to produce energy. This activity is already incor-porated in many carbon offsets programs and renewable energy programs. However, the capital, operation, and maintenance costs of changing manure handling systems can present a significant hurdle. Overcoming it could require external investment and changes in energy sector policy and business models.

Feeding strategies for swine, with the possible exception of reducing dietary protein, do not appear as promising. However, many manure management strategies do. These strategies include increasing manure removal frequency, separating solids and liquids, optimizing bedding materi-als for dry manure management, covering manure storage, and composting. The mitigation potential and financial viability of these strategies should be further researched.

5. U.S. EPA, 2011.6. U.S. EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2010 (Washington, D.C.: U.S. EPA, 2012).7. U.S. EPA, 2011.8. Ibid.9. U.S. EPA, 2011; U.S. Department of Agriculture (USDA): U.S. Beef and Cattle Industry: Background Statistics and Information (Washington, D.C.: USDA, 2011).

0

20

40

60

80

100

120

140

160

grazed land (net=CH4+N2O-CO2)

manure (CH4+N2O)

enteric (CH4)

Beef cattl

e

Dairy ca

ttle

Swine

Horses

Poultry

SheepGoats

Figure 3. Greenhouse gas emissions by livestock source in 2008.Source: USDA, 2011 (note 9).

133.8 136.5 139.0 141.4 143.8 143.4 142.6 141.3

31.7 42.4 47.9 48.4 52.7 51.8 50.7 52.0

0 25 50 75

100 125 150 175 200 225

1990 2000 2005 2006 2007 2008 2009 2010

Tg C

O2e

Year

Enteric fermentation Manure management Other

202.6 200.8 195.9 193.9 186.7 172.9

202.9 202.2

Figure 2. Sources of methane emissions from U.S. agriculture.Source: U.S. EPA, 2012 (note 6).

Greenhouse Gas Mitigation Opportunities for Livestock Management in the United States

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Covering manure may have only moderate costs, and composting could generate money through production of a value-added fertilizer for off-site marketing. Anaerobic digestion, although costly, also has a high mitigation potential and is ready for use in programs similar to those developed for dairy cattle manure digesters.

Tables 1 and 2 provide a qualitative summary and a comparison of the reviewed mitigation practices. The action category indicates whether the management action

• is ready for integration into programs and protocols as a mitigation practice and is of high or moderate priority, given its potential;

• is likely to have significant mitigation potential but is supported by little research, making it a research priority;• appears to have low mitigation potential or significant implementation barriers and thus is a low priority for research

or action; or• is supported by too little research to make a recommendation and is therefore uncertain.

Table 1. Summary of beef and dairy mitigation practices, based on the opinions of expert authors.Mitigation potential Amount of research Expert confidence Potential expense Action category

Grazing systems changesChange from traditional pasture grazing to managed pasture

Some soil C benefits and efficiency of animal production

Low Moderate Moderate Ready; high priority

Change from traditional pasture grazing to intensive feedlot system

Will likely produce ~50% reduction in enteric CH4, but more research needed on leakage issues

Significant Significant Significant Research priority

Feeding strategiesLipid supplements Unclear Moderate Significant Low Research priorityIntake modification/measurement in association with reduced CH4 production

Unclear Low Low Unknown Research priority

Ionophores 10% to 25% reduction in CH4, but duration may be limited*

Significant Significant Low Research priority

Halogenated compounds Low Low Moderate Very high Low priorityPlant compounds Unclear Low Low High at effective doses Research priorityProbiotics and organic acids Unclear Low Low High at effective doses Research priority

Vaccination Unclear Low Low High Low priorityImproved genetics Unclear Moderate Low High (long term

investment 10–20 years)

Research priority

Manure managementManure cooling of 10°C Unknown Low Low High Low priorityAltering manure pH Unknown Low Low High Low priorityCompaction Theoretically high, but

little dataLow Moderate Low Research priority

Frequent spreading Unknown Low Low Low Research priorityMethane use for energy – methane digesters

High Moderate High Very high Ready; high priority and research priority

Manure aeration High Moderate Moderate High Research priority

* Less is known about the potential to “cycle” the ionophore (e.g., 6 weeks on, 6 weeks off).

Greenhouse Gas Mitigation Opportunities for Livestock Management in the United States

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Table 2. Summary of swine mitigation practices, based on the opinions of expert authors.Mitigation potential Amount of research Expert confidence Potential expense Action category

Feeding strategiesLower protein diet 10% reduction in protein ~ 10% reduction in

CH4; and potential to lower N2O not studiedLittle Low Low Research priority

Feed ingredients Unclear Little Low Low UncertainOil additives Unclear Little Low Low UncertainManure managementReduced time in pit 30% reduction in CH4; but often limited by

when can move manureModerate Uncertain Ready; moderate

priorityFloor openness Unclear Little Low High Low prioritySolid-liquid separation Unclear Little Low High Research prioritySolid manure storage Unclear Little Low Significant UncertainBedding materials N2O uncertain; CH4 30% Little Low Uncertain Research priorityLower temperature and better ventilation

10–20°C drop ~ 20%–60% for CH4; unclear for N2O; increase CO2 from energy need

Moderate Moderate High Uncertain

Covering manure storage

Can be significant depending on cover type, ranges from 88% reduction to an increase

Moderate but all with different cover types

Moderate Moderate Research priority

Composting Significant but variable Moderate Moderate Potential profit Research priorityAnaerobic digestion Significant High High High Ready; high priority

All of these management practices need further study and a comparison of costs. Emissions reductions from manure methane capture systems can be measured directly, but quantifying emissions reductions from other livestock systems will likely require the use of various modeling approaches. A wide range of models are being tested and used for national inventory quantification concurrently with the development of a number of farm-scale accounting tools for carbon offsets programs and corporate supply chain life-cycle assessment (LCA) tools. These models and system-level tools can be helpful in ensuring that management changes do not inadvertently increase one greenhouse while reducing another.

Accounting approaches for tracking GHG emissions from livestock are also in development. Carbon offset protocols are designed to track changes in emissions resulting from a specific project (or management change). Many livestock-related offset protocols have been approved or are in development (table 3). LCAs, on the other hand, are used to assess changes in a production system or supply chain for a product; they indicate emissions hot spots and facilitate emissions comparisons across supply chains, products, and time. As yet, LCA methods have little consistency across applications.

Table 3. Livestock protocols developed by program and registries.Protocol/initiative Emissions scope Status

Alberta Offset System*

Dairy Cattle Emissions ReductionEnteric CH4, manure CH4, N2O Approved

Innovative Feeding of Swine and Storing and Spreading of Swine Manure Manure CH4 and soils N2O ApprovedBeef Feeding – Edible Oils Enteric CH4 ApprovedBeef Reduced Days on FeedBeef Reducing Age to HarvestSelecting for Low Residual Feed Intake in Beef

All 3 protocols:enteric CH4, manure CH4, N2O

ApprovedApprovedPending

Modification of Alberta Offset System Livestock GHG protocols for U.S. Enteric CH4, manure CH4, N2O In development (ACR)Development of a Modular Methodology for Quantification and Measurement of GHG Emission Reductions from Ruminant Livestock Production

Enteric CH4, manure CH4, N2O In development (ACR)

Soil Carbon Sequestration through Rangeland Management CO2, CH4, N2O In development by Environmental Defense Fund, UC Berkeley, and other organizations

* See www.carbonoffsetsolutions.ca.

In summary, livestock management has a few well-researched and ready-for-action opportunities for making measurable and substantial methane reductions. These more established opportunities, such as anaerobic digesters, tend to be costly. The mitigation potential and financial viability of many other potentially significant management opportunities require further research and pilots before widespread implementation.